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7-2
Chapter 7. Modbus RTU Communication Functions
z
Settings
For Modbus communication, use the following settings.
Item name
Settings
Initial value
Station address
0: No communication
1 to 127
0
Transmission speed
1: 9600 bps
2: 19200 bps
3: 38400 bps
4: 57600 bps
5: 115200 bps
2
Data type (parity)
0: Even parity
1: Odd parity
2: No parity
0
Data type
(Stop bits)
0: 1 bit
1: 2 bits
0
Minimum response time
1 to 250 ms
3
Handling Precautions
•
The communication settings cannot be changed through RS-485
communication.
•
Configure the settings above according to the characteristics of the host
unit and RS-232C/RS-485 communication converter used.
z
Communication procedure
The communication procedure is as follows.
(1) An instruction message is sent from the host unit (master station) to one unit
of this device (slave station).
(2) The slave station receives the instruction message and executes the read or
write process according to the contents of the message.
(3) Furthermore, the slave station sends a response message appropriate for the
process details.
(4) The master station receives the response message.
Handling Precautions
•
Multiple protocols such as CPL, Modbus ASCII, and Modbus RTU cannot be
used together on the same RS-485 transmission line.